The main objective of the present proposal is to understand how androgens reorganize the synaptic relations between androgen-sensitive spinal motoneurons and their afferents. The spinal nucleus of the bulbocavernosus (SNB) is a group of androgen-sensitive motoneurons which offer special advantages for studying this question. Steroids regulate the size and dendritic length of SNB neurons and there is recent evidence suggesting that androgens may also regulate the afferent input to the SNB. Thus, we plan to characterize the synaptic relationship of afferents with SNB cell bodies and processes, to identify neurons of origin of SNB afferents, and to determine whether afferent neurons accumulate steroids. Electron microscopic analysis of retrogradely labeled SNB neurons and their processes in males will provide an assessment of the organization of synaptic input to the cell body, and to proximal, middle, and distal dendrites of these motoneurons under varying androgen environments. Using a combination of retrograde and anterograde tract tracing, immunocytochemistry, and steroid autoradiography, we will characterize the chemical nature and origin of SNB afferents, and their ability to accumulate sex steroids. This analysis of SNB afferents is expected to shed significant light on the question of how steroids modulate the synaptic inputs to steroid-sensitive neurons in the adult CNS.